Merging elements of dystopia, steampunk, and fantasy, this magnetic middle-grade debut imagines an alien world where 13-year-old Piper survives by working as a scrapper, salvaging artifacts left behind by meteor storms. Her life transforms when she rescues a mysterious girl in the aftermath of one such storm: Anna is brilliant yet disoriented, and she sports a tattoo signifying that she is held under the protection of the king of the Dragonfly territories. Piper knows that a reward awaits her if she returns Anna safely to her home. Yet passage on board the 401, a mile-long armored train, is beyond their grasp, and Anna is also being pursued by a ruthless, ominous man. With a setting drawn from an industrial revolution still in birthing pains, Johnson's narrative is marked by colloquial language and blends societal decay with a sense of burgeoning technological innovation. Piper and her new ally, the enigmatic Gee, exhibit maturity and resourcefulness at every turn in a page-turner that defies easy categorization and ought to have broad appeal. Ages 10–up. Agent: Sara Megibow, Nelson Literary Agency. (Mar.)